The area has two main parts. The northern 'Dark Peak' is where most of the moorland is found. Its geology is gritstone. The southern 'White Peak' is where most of the population lives: its geology is mainly limestone.

Earth movements after the Carboniferous period resulted in the up-doming of the area. This resulted in the dome-like shape.[7] The shale and sandstone were worn away until limestone was exposed. At the end of this period, the Earth's crust sank here which led to the area being covered by sea, depositing a variety of new rocks.[8]

Some time after its deposition, mineral veins were formed in the limestone. These veins and rakes have been mined for lead since Roman times.[8]

The Peak District was covered by ice during at least one of the ice ages of the last 2 million years. Glacial meltwaters eroded a complex of sinuous channels along the margin of the Peak District during this period.[9] Glacial meltwaters helped form many of the caves in the limestone area.[10] Wild animal herds roamed the area, and their remains have been found in several of the local caves.[8]

The different types of rock that lie beneath the soil strongly influence the landscape. They determine the vegetation and so the animals that will live in the area.[11] Limestone has fissures (cracks) and is soluble in water, so rivers carve deep, narrow valleys. These rivers then often find a route underground, creating cave systems. Millstone Grit on the other hand is insoluble but porous, so it absorbs water. Water moves through the grits until it meets the less porous shales beneath, creating springs when it reaches the surface again. The shales are friable and easily attacked by frost. They form areas where landslides may occur, as on Mam Tor.[7]